Supercapacitors, also known as electrochemical capacitors, are attracting much research attention owing to their high power density, long-term cycling stability, as well as exceptional safety compared with rechargeable batteries, although the globally accepted quantitative benchmarks on the power density, cycling stability, and safety are yet to be established. However, it should be noted that the supercapacitors generally exhibit low energy density, which cannot satisfy the demands where both high energy density and power density are needed. To date, various methods have been employed to improve the electrochemical performances of supercapacitors. Among them, introducing redox additives (or redox mediators) into conventional aqueous electrolyte is regarded as one of the most promising strategies. The redox additives in aqueous electrolyte are widely demonstrated to be able to increase the charge storage capability via redox transformation and thus enhance the electrochemical performances. Herein, we present a brief review on the classification, state-of-the-art progress, challenges, and perspectives of the redox additives in aqueous electrolyte for high performance supercapacitors.

Ultrasonic irradiation was applied to the synthesis of polyaniline (PANI) nanofibers in a conventional oxidant dropwise addition fashion. The secondary growth of the initially formed PANI nanofibers into thick fibers with uneven surfaces and the agglomeration of the thick fibers into irregular particles that occurred in the case of magnetic stirring were successfully prevented in the presence of ultrasonic irradiation, and the nanofibers were preserved even hours after the secondary addition of aniline and ammonium peroxydisulfate to the reaction media. This makes the method one of the facile ways of synthesizing PANI nanofibers.

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A new family of silver(I)-lanthanide(III) heterometallic-organic frameworks having the formula [AgLn(bpdc)2] (Ln = Eu (1), Tb (2), Sm (3), Dy (4), Y (5), Yb (6), Er (7), Ho (8); H2bpdc = 2,2'-bipyridine-3,3'-dicarboxylic acid), each of which crystallizes in the monoclinic space group C2/c with Z = 4, has been hydrothermally synthesized. The compounds were characterized by means of IR, elemental analysis, thermogravimetric-differential thermal analysis, and powder X-ray diffraction (XRD), wherein compounds 1, 2, and 4-8 were structurally characterized. The powder XRD and single-crystal structures of the title compounds indicate that all the compounds are isostructural and feature a three-dimensional (3-D) open framework. In the structures of the compounds, bpdc(2-) ligands link Ln(3+) through their carboxylic groups, resulting in the formation of a one-dimensional {Ln(bpdc)2}n infinite chain along the c direction. The adjacent chains are then connected to each other through the coordination interaction between Ag(+) and the pyridyl N atoms of bpdc(2-) ligands from the chains, resulting in a 3-D (2,4,6)-connected open framework with (4(11)·6(4))(4(3)·8(2)·10)(8)2 topology. The compounds show remarkable good thermally stability up to 370 °C because neither aquo ligands nor lattice water molecules exist in the composition of the compounds. The photoluminescent properties of compounds 1 and 2 were studied in detail. The energy level of the triplet states of the ligand H2bpdc 21,505 cm(-1) (465 nm) was determined based on the 77 K emission spectrum of the compound [Gd2(bpdc)3(phen)2(H2O)2]·6H2O 9. The (5)D0 and (5)D4 emission lifetimes (1.58 and 1.76 ms) and the overall quantum yields (21% and 22%) were determined for the compounds 1 and 2, respectively.

The well-ordered assembly of collagen molecules on mica surface has attracted extensive attention because it has great potential applications or can be served as a model system for study on the assembly process. Although the epitaxially guided collagen assembly mediated by potassium ion on mica surface has been reported several times over these years, specific effects of anions in this field has never been surveyed and discussed before now. In this work, atomic force microscopy was employed to visually follow the assembly of collagen on mica surface mediated by three kinds of Mg(2+) salts with different anions, including MgAc2, MgSO4, and MgCl2. It was found that at high ionic concentration anions could critically affect the interaction between collagen microfibrils and mica surface and accordingly resulted in different structures. Almost parallelly aligned collagen fibrils in one direction were achieved for acetates, sparse and small fibrils in two main directions rotated by 120° were acquired for sulfate, while flat film with some defects was obtained for chloride, respectively. The Hofmeister series and Collins' model were used to interpret the results. This study would be useful for controlling the morphologies of assembled collagen on a surface.